The present invention relates generally to telecommunications networks, and more particularly to a method and apparatus for performing directory number/Internet Protocol (IP) address resolutions to facilitate voice over IP communications.
Though originally designed for the transmission of data, Internet Protocol (IP) networks are increasingly being used as an alternative voice communication tool. In recent years there have been many advancements and developments in the area of IP telephony, which refers to communication services e.g. voice, facsimile, and/or voice-messaging applications that are transported via an Internet Protocol network, rather than the Public Switched Telephone Network (PSTN). Telephone subscribers are drawn to IP telephony as an alternative to traditional forms of communications, especially for long-distance telephone calls, because it can offer cost savings relative to the PSTN. With the use of IP telephony, subscribers can bypass long-distance carriers and their per-minute usage rates and run their voice traffic over an IP network, such as the Internet, for a flat monthly Internet access fee.
Presently, a PSTN caller cannot place a voice call over an IP network to another PSTN phone or terminal by simply dialling the called directory number. This is because the PSTN is not set up to map a directory number to an IP address, which is necessary for PSTN-IP network interaction.
In today""s IP networks, an IP gateway provides the necessary connectivity between an IP network and the PSTN. Typically, a long distance call initiated by a PSTN caller to a PSTN called party over an IP network would involve the following steps: (i) a PSTN call to a local IP gateway; (ii) an IP call to a far-end IP gateway; and (iii) a PSTN call from the far-end IP gateway to the called party. The function of the IP gateway is to perform the necessary translations of addressing and routing information between the IP network and the PSTN and vice versa for the call to reach its intended destination.
To reduce costs, it is often desirable to select a far-end IP gateway that would result in the cheapest call from the gateway to the called party. Other criteria, such as reliability and quality may also be used to select one far-end IP gateway over another. However, IP gateways may be scattered around the world, run by possibly independent, widely distributed service providers. The problem is that given a directory number for a called party, how does the network know which far-end IP gateway meets the criteria set by the calling party for the call?
Several solutions have been put forward to provide directory number/IP address resolution for IP gateways. For example, centralized databases connected to the IP network can be queried to provide the necessary mappings between directory numbers to IP addresses. An example of the implementation of a centralized database approach is set out in Jonathan Rosenberg and Henning Schulzrinne, xe2x80x9cInternet Telephony Gateway Locationxe2x80x9d Bell Laboratories, Columbia University, 1998. However, a centralized database approach is not viable in the context of most large IP networks, such as the Internet. First, a failure in the database could be catastrophic to the network. Second, it can be an unmanageable process to maintain records in one centralized database for all IP gateways scattered around the world.
Global solutions with distributed telephone number hierarchy for information retrieval have also been put forward. These solutions require Trusted, Third Party, Top Level Service Providers. These entities are known as an Internet Telephony Directory Service Providers (ITDSPs). However, there is presently no common infrastructure in place to implement these solutions with relative speed.
Distributed database solutions, which scatter information concerning IP gateways across the IP network, have also been considered. However, the forms of distributed databases that have been proposed all suffer from similar scalability problems due to the difficulty of organizing and searching through the distributed data entries.
Since it is likely that the current PSTN will remain the dominant medium of carrying telephony services for quite some time, the present invention solves the problem of directory number/IP address resolution by treating an IP gateway as an extension of the PSTN rather than solely as an IP based entity.
The present invention takes advantage of existing TDM protocols and infrastructure to request and retrieve IP gateway information without the need for special hardware or third-party services. By using existing TDM infrastructure to resolve DN/IP address queries, the present invention does not suffer from the scalability problems inherent in other DN/IP address resolution solutions.
The steps of a typical implementation of the present invention include: (i) the user initiating a call from a regular telephone by dialling a directory number (DN) of a called party but requesting an IP-based network route; (ii) upon call initiation, an originating Time-Division Multiplex (TDM) switch servicing the user forwards a message over a TDM network requesting the IP address of an IP gateway servicing the called party (the far-end IP gateway), (iii) the terminating TDM switch servicing the called party retrieves IP address of the far-end IP gateway corresponding to the DN, and forwards that IP address to the originating TDM switch over the TDM network; (iv) the originating exchange switch receives the IP address of the far-end IP gateway and forwards the IP address to a near-end IP gateway; (v) using the IP address, the near-end IP gateway establishes a speech path over an IP-based network that terminates at the far-end gateway; (vi) far-end IP gateway receives call and completes it to the DN.
IP gateway information can be retrieved to enable IP calls to be made between two end nodes of a private network, two end nodes of a public network, or any combination of end nodes in a public and a private network.
In one embodiment of the present invention, the QSIG and QVPN (QSIG Virtual Private Network) signalling protocols are used to request and retrieve IP gateway information across a TDM network between an originating TDM switch, a terminating TDM switch, and any necessary TDM transit switches between the end switches. QSIG is a signalling system protocol used between interconnected Private Integrated Services Network Exchanges in a Private Integrated Services Network. QVPN is used to implement the service of the present invention between public TDM switches.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.